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PowerShell DSL Module Considerations

Just a quick note to mention a couple of things I’ve come across with PowerShell modules that encapsulate DSLs (Domain Specific Languages, specifically WPFBot3000).

PowerShell Command Name Warnings

PowerShell modules have always issued warnings if they contain commands that don’t use approved verbs. What’s fun with modules for DSLs is that the commands in general don’t use verbs at all. Since these commands aren’t “proper”, you might expect a warning. You won’t get one, though.

PowerShell Module Autoloading

PowerShell modules have had autoloading since v3.0. Simply put, if you use a cmdlet that isn’t present in your session PowerShell will look in all of the modules in the PSModulePath and try to find the cmdlet somewhere. If it finds it, PowerShell imports the module quietly behind the scenes.

This doesn’t work out of the box with DSLs. The reason is simple.

DSLs generally have commands that aren’t in the verb-noun form that PowerShell is expecting for a cmdlet, so it doesn’t try to look for the command at all.

The fix for this is simple (for WPFBot3000, at least). All I’ve done is replace the two top-level commands (Window and Dialog) with well-formed cmdlet names (New-WPFBotWindow and Invoke-WPFBotDialog). Then, I create aliases (Window and Dialog) pointing to these commands.

Now that I think of it, I’m not sure why that works. If PowerShell is looking for the aliases, why wasn’t it finding the commands? Nevertheless, it works.